Method and apparatus for encoding and decoding image

ABSTRACT

An apparatus and method for encoding and decoding an image are provided. The image decoding method includes (a) decoding luma blocks according to a predetermined decoding mode of each of the luma blocks, and (b) decoding chroma blocks according to the predetermined decoding mode of each of the luma blocks.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Continuation of International Application No.PCT/KR2006/002786, filed Jul. 14, 2006 and claims the benefit of KoreanPatent Application No. 10-2005-0064453, filed on Jul. 15, 2005, in theKorean Intellectual Property Office, the disclosures of which areincorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image compression and restoration, andmore particularly, to an apparatus and method for encoding and decodingan image in order to compress and restore the image comprising lumablocks and chroma blocks.

2. Description of the Related Art

If an image to be compressed is expressed in a red (R), green (G), andblue (B) color space, three RGB color components of the image have thesame resolution since the three RGB color components are equallyimportant for the image.

A human visual system (HVS) is more sensitive to luma than chroma.Therefore, a luma component has a higher resolution than a chromacomponent in order to express the image.

In order to compress and restore an image expressed using the lumacomponent and the chroma component, which are separate from each other,there is an issue as to which encoding mode (or decoding mode) is usedto encode (or decode) the luma component and chroma component.

SUMMARY OF THE INVENTION

The present invention provides an image decoding method of decoding achroma block according to a decoding mode determined based on a decodingmode of a luma block.

The present invention also provides an image decoding method of decodinga chroma block according to a predetermined decoding mode of each chromablock.

The present invention also provides an image encoding method of encodinga chroma block according to an encoding mode determined based on anencoding mode of a luma block.

The present invention also provides an image encoding method of encodinga chroma block according to a predetermined encoding mode of each chromablock.

The present invention provides an image decoding apparatus for decodinga chroma block according to a decoding mode determined based on adecoding mode of a luma block.

The present invention also provides an image decoding apparatus fordecoding a chroma block according to a predetermined decoding mode ofeach chroma block.

The present invention also provides an image encoding apparatus forencoding a chroma block according to an encoding mode determined basedon an encoding mode of a luma block.

The present invention also provides an image encoding apparatus forencoding a chroma block according to a predetermined encoding mode ofeach chroma block.

According to an aspect of the present invention, there is provided animage decoding method comprising: (a) decoding luma blocks according toa predetermined decoding mode of each luma block; and (b) decodingchroma blocks according to the predetermined decoding mode of each lumablocks.

According to another aspect of the present invention, there is providedan image decoding method comprising: (a) decoding luma blocks accordingto a predetermined decoding mode of each luma block; and (b) decodingchroma blocks according to a predetermined decoding mode of each chromablock.

According to another aspect of the present invention, there is providedan image encoding method comprising: (a) encoding luma blocks accordingto a predetermined encoding mode of each luma block; and (b) encodingchroma blocks according to the predetermined encoding mode of each lumablock.

According to another aspect of the present invention, there is providedan image encoding method comprising: (a) encoding luma blocks accordingto a predetermined encoding mode of each luma block; and (b) encodingchroma blocks according to a predetermined encoding mode of each chromablock.

According to another aspect of the present invention, there is providedan image decoding apparatus comprising: a first decoding unit decodingluma blocks according to a predetermined decoding mode of each lumablock; and a second decoding unit decoding chroma blocks according tothe predetermined decoding mode of each luma block.

According to another aspect of the present invention, there is providedan image decoding apparatus comprising: a first decoding unit decodingluma blocks according to a predetermined decoding mode of each lumablock; and a second decoding unit decoding chroma blocks according to apredetermined decoding mode of each chroma block.

According to another aspect of the present invention, there is providedan image encoding apparatus comprising: a first encoding unit encodingluma blocks according to a predetermined encoding mode of each lumablock; and a second encoding unit encoding chroma blocks according tothe predetermined encoding mode of each luma block.

According to another aspect of the present invention, there is providedan image encoding apparatus comprising: a first encoding unit encodingluma blocks according to a predetermined encoding mode of each lumablock; and a second encoding unit encoding chroma blocks according to apredetermined encoding mode of each chroma block.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a block diagram of an image encoding/decoding apparatusaccording to an embodiment of the present invention;

FIG. 2 is a block diagram of an encoding unit illustrated in FIG. 1according to an embodiment of the present invention;

FIG. 3 is a block diagram of a decoding unit illustrated in FIG. 1according to an embodiment of the present invention;

FIGS. 4A, 4B, and 4C are diagrams illustrating macroblocks of images ina 4:2:0 format, a 4:2:2 format, and a 4:4:4 format, respectively;

FIG. 5 is a block diagram of an image encoding apparatus according to anembodiment of the present invention;

FIGS. 6 through 8 are diagrams for explaining motion information (MI);

FIG. 9 is a block diagram of an image decoding apparatus according to anembodiment of the present invention;

FIGS. 10 (Parts (A) and (B)) are diagrams for explaining the principleof encoding/decoding an image using a 1 motion vector (MV);

FIG. 11 is a flowchart illustrating an image encoding method accordingto an embodiment of the present invention;

FIG. 12 is a flowchart illustrating an image decoding method accordingto an embodiment of the present invention;

FIGS. 13 through 15 are diagrams for explaining the principle ofencoding/decoding an image using a 4 MV according to an embodiment ofthe present invention;

FIG. 16 is a flowchart illustrating an image encoding method accordingto another embodiment of the present invention;

FIG. 17 is a flowchart illustrating an image decoding method accordingto another embodiment of the present invention;

FIGS. 18 (Parts (A), (B), and (C)) are diagrams for explaining theprinciple of encoding/decoding an image using a 4 MV according toanother embodiment of the present invention;

FIG. 19 is a flowchart illustrating an image encoding method accordingto another embodiment of the present invention;

FIG. 20 is a flowchart illustrating an image decoding method accordingto another embodiment of the present invention; and

FIGS. 21 (Parts (A) and (B)) are diagrams for explaining the principleof encoding/decoding an image using a 4 MV according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown.

FIG. 1 is a block diagram of an image encoding/decoding apparatusaccording to an embodiment of the present invention. The imageencoding/decoding apparatus includes an encoding unit 110 and a decodingunit 120.

The encoding unit 110 encodes an image input through an input terminalIN1, generates a bitstream, and transmits the bitstream to the decodingunit 120. The image may be expressed using a luma component and a chromacomponent, which are separated from each other rather than an imageexpressed in a RGB color space. An image having the luma componentcomprises one or more luma blocks. An image having the chroma componentcomprises one or more chroma blocks. The image may comprise a pluralityof frames in temporal sequence.

The decoding unit 120 decodes the bitstream transmitted from theencoding unit 110, restores the image, and outputs the restored imagethrough an output terminal OUT1. If the decoding unit 120 compresses theimage without any loss, the restored image is completely identical tothe image input through the input terminal IN1. Similarly, if theencoding unit 110 lossy-compresses the image, the restored image is notidentical to but similar to the image input through the input terminalIN1.

The image is encoded and decoded in the unit of a macroblock. In detail,the image can be compressed and restored in the unit of a macroblock.The macroblock comprises one or more luma blocks and one or more chromablocks.

FIG. 2 is a block diagram of the encoding unit 110 illustrated in FIG. 1according to an embodiment 110A of the present invention. Referring toFIG. 2, the encoding unit 110 comprises a motion estimating unit 212, areference image storing unit 214, a motion compensation unit 216, aspatial converting unit 218, a quantizing unit 220, a dequantizing unit222, an inverse spatial converting unit 224, a rearranging unit 226, azero encoding unit 228, and an entropy encoding unit 230.

The encoding unit 110 can encode an image input through an inputterminal IN2 according to an inter mode or an intra mode. The inputterminal IN2 is identical to the input terminal IN1 illustrated in FIG.1.

In the inter mode, an image is encoded (or decoded) using motioncompensation. In the intra mode, an image is encoded (or decoded)without motion compensation.

If the encoding unit 110 encodes an image at the inter mode, all theconstituents from the motion estimating unit 212 to the entropy encodingunit 230 are operated. To the contrary, if the encoding unit 110 encodesthe image in the intra mode, the motion estimating unit 212, the motioncompensation unit 216, the dequantizing unit 222, and the inversespatial converting unit 224 are not operated.

The operation of the encoding unit 110 according to the inter mode willnow be described. For convenience of explanation, the operation of theencoding unit 110 that performs block-based motion compensation will nowbe described.

The motion estimating unit 212 finds an m*n block that is the closestmatch to a target block (the target block is the m*n block in which mand n are natural numbers, and the m*n block is a block in which mpixels are arranged in n rows) in a reference frame. The found block iscalled a prediction block.

The target block is a block to be currently encoded. The reference frameindicates one or more previously encoded frames. The reference frame isstored in the reference image storing unit 214. The motion estimatingunit 212 reads the reference frame stored in the reference image storingunit 214.

The motion compensating unit 216 subtracts the prediction block from thetarget block in order to generate a residue block. The motioncompensating unit 21 6 generates a motion vector (MV) indicating arelative location of the target block to the prediction block.

As described above, the target block, the prediction block, the residueblock are all the m*n blocks and comprise pixel values.

The spatial converting unit 218 converts the pixel values intofrequencies. In detail, the spatial converting unit 218 concentratesdata forming the residue block in a low frequency band.

In detail, the spatial converting unit 218 can perform a discrete cosinetransform (DCT). The meaning of the DCT is described in detail in“Discrete Cosine Transform” published in 1990 by K. R. Rao and P. Yip atthe Academic Press. The spatial converting unit 218 converts m*n pixelvalues included in the residue block into m*n DCT coefficients.

The quantizing unit 220 quantizes the DCT coefficients generated by thespatial converting unit 218. The quantizing unit 220 can perform alinear quantization and a non-linear quantization. In particular, thequantizing unit 220 performs the linear quantization so that the DCTcoefficients close to 0 can be 0.

The dequantizing unit 222 and the inverse spatial converting unit 224are operated in order to generate a reference frame to be used when anext-to-be-encoded target block is encoded.

The dequantizing unit 222 dequantizes the quantized DCT coefficientsperformed by the quantizing unit 220. The spatial converting unit 224performs inverse DCT (IDCT) on the result of the dequantizationperformed by the dequantizing unit 222. Therefore, the inverse spatialconverting unit 224 generates a residue block.

In this case, the residue block and the prediction block found by themotion estimating unit 212 are added together in order to restore thetarget block. The restored target bock is stored in the reference imagestoring unit 214 as a part of the reference frame.

The rearranging unit 226 scans the results quantized by the quantizingunit 220 in a zigzag shape and rearranges the scanned results. The zeroencoding unit 228 can perform run-level (RL) encoding. In detail, thezero encoding unit 228 can more simply rearrange the rearranged values.In more detail, the zero encoding unit 228 can express continuously therearranged values (run, level). The run denotes the number of 0s in thefront of the rearranged values. The level denotes the rearranged valuesother than 0.

The entropy encoding unit 230 entropy-encodes the results encoded by thezero encoding unit 228. Also, the entropy encoding unit 230entropy-encodes the motion vector generated by the motion compensatingunit 216. The results entropy-encoded by the entropy encoding unit 230are output as one bitstream through an output terminal OUT2.

The operation of the decoding unit 110 according to the intra mode willnow be described.

The spatial converting unit 218 converts a pixel value of the imageinput through the input terminal IN2 into a frequency. In detail, thespatial converting unit 218 concentrates data forming the image in a lowfrequency band. In more detail, the spatial converting unit 218 canperform the DCT.

The quantizing unit 220 quantizes the DCT coefficients produced by thespatial converting unit 218. The quantizing unit 220 can perform alinear quantization or a non-linear quantization. In particular, thequantizing unit 220 performs the non-linear quantization, so that theDCT coefficients close to 0 can be 0.

The rearranging unit 226 scans the results of the quantization performedby the quantizing unit 220 in a zigzag shape and rearranges the scannedresults. The zero encoding unit 228 can perform run-level (RL) encoding.In detail, the zero encoding unit 228 can more simply rearrange therearranged values. In more detail, the zero encoding unit 228 cancontinuously express the rearranged values (run, level). The run denotesthe number of 0s in the front of the rearranged values. The leveldenotes the rearranged values other than 0.

The entropy encoding unit 230 entropy-encodes the results encoded by thezero encoding unit 228. The results of the entropy-encoding performed bythe entropy encoding unit 230 are output as one bitstream through anoutput terminal OUT2.

FIG. 3 is a block diagram of the decoding unit 120 illustrated in FIG. 1according to an embodiment 120A of the present invention. Referring toFIG. 3, the decoding unit 120 comprises an entropy decoding unit 312, azero decoding unit 314, an inverse rearranging unit 316, a dequantizingunit 318, an inverse spatial converting unit 320, a motion estimatingunit 322, and a reference image storing unit 324.

The decoding unit 120 can decode a bitstream input through an inputterminal IN3 according to an inter mode or an intra mode. The bitstreaminput through the input terminal IN3 can be the bitstream output throughthe output terminal OUT2 illustrated in FIG. 2.

If the decoding unit 120 decodes the bitstream in the inter mode, allthe constituents, from the entropy decoding unit 312 to the referenceimage storing unit 324, are operated. To the contrary, if the decodingunit 120 decodes the bitstream at the intra mode, the motion estimatingunit 322 is not operated.

The operation of the decoding unit 120 according to the inter mode willnow be described.

The entropy decoding unit 312 entropy-decodes the bitstream inputthrough the input terminal IN3, so that the entropy decoding unit 312can extract results of the RL-decoding performed by the zero decodingunit 228 and can extract the motion vector generated by the motioncompensating unit 216 from the bitstream input through the inputterminal IN3.

The zero decoding unit 314 performs the RL-decoding. The inverserearranging unit 316 generates the results of the quantization performedby the quantizing unit 220.

The dequantizing unit 318 dequantizes the results generated by thequantizing unit 220 input from the inverse rearranging unit 316. Theinverse spatial converting unit 320 performs an inverse space conversion(e.g., the IDCT) on the results of the dequantization performed by thedequantizing unit 318. The inverse spatial converting unit 318 generatesa residue block.

The motion estimating unit 322 finds a prediction block in a referenceframe stored in the reference image storing unit 324 using the motionvector extracted from the entropy decoding unit 312.

The residue block generated by the inverse spatial converting unit 318and the prediction block found by the motion estimating unit 322 areadded together in order to restore a target block. The restored targetblock is output through the output terminal OUT3. The restored targetblock is stored in the reference image storing unit 324 as a part of thereference frame.

The operation of the decoding unit 120 according to the intra mode willnow be described.

The entropy decoding unit 312 extracts the results of the RL-decodingperformed by the zero decoding unit 228 from the bitstream input throughthe input terminal IN3.

The zero decoding unit 314 performs the RL-decoding. The inverserearranging unit 316 generates the results of quantization performed bythe quantizing unit 220.

The dequantizing unit 318 dequantizes the results generated by theinverse rearranging unit 316. The inverse spatial converting unit 320performs the inverse space conversion (e.g., the IDCT) on the results ofdequantization performed by the dequantizing unit 318, so that theinverse spatial converting unit 318 restores an image and outputs therestored image through an output terminal OUT4. The restored image canbe stored in the reference image storing unit 324.

FIGS. 4A, 4B, and 4C are diagrams illustrating macroblocks of images ina 4:2:0 format, a 4:2:2 format, and a 4:4:4 format, respectively.

Referring to FIG. 4A, a macroblock of a 4:2:0 format image comprisesfour luma blocks Y, one blue chroma block Cb, and one red chroma blockCr. Each of the luma blocks Y, the blue chroma block Cb, and the redchroma block Cr is an 8*8 block. In detail, each of the luma blocks Y,the blue chroma block Cb, and the red chroma block Cr has eight pixelsin eight rows (=64 samples).

Referring to FIG. 4B, a macroblock of a 4:2:2 format image comprisesfour luma blocks Y, two blue chroma blocks Cb, and two red chroma blocksCr. Each of the luma blocks Y, the blue chroma blocks Cb, and the redchroma blocks Cr is an 8*8 block. In detail, each of the luma blocks Y,the blue chroma blocks Cb, and the red chroma blocks Cr has eight pixelsin eight rows (=64 samples).

Referring to FIG. 4C, a macroblock of a 4:4:4 format image comprisesfour luma blocks Y, four blue chroma blocks Cb, and four red chromablocks Cr. Each of the luma blocks Y, the blue chroma blocks Cb, and thered chroma blocks Cr is an 8*8 block. In detail, each of the luma blocksY, the blue chroma blocks Cb, and the red chroma blocks Cr has eightpixels in eight rows (=64 samples).

FIG. 5 is a block diagram of an image encoding apparatus according to anembodiment of the present invention. Referring to FIG. 5, the imageencoding apparatus comprises a first encoding unit 512, a secondencoding unit 514, a third encoding unit 516, and a bitstream generatingunit 518.

The first encoding unit 512 and the second encoding unit 514 arerealized as the encoding unit 110 comprising the motion estimating unit212, the reference image storing unit 214, the motion compensation unit216, the spatial converting unit 218, the quantizing unit 220, thedequantizing unit 222, the inverse spatial converting unit 224, therearranging unit 226, the zero encoding unit 228, and the entropyencoding unit 230 as illustrated in FIG. 2.

In detail, the first encoding unit 512 indicates the encoding unit 110that encodes the luma block Y input through the input terminal IN2. Thesecond encoding unit 514 indicates the encoding unit 110 that encodesthe chroma block Cb or Cr input through the input terminal IN2.

The first encoding unit 512 encodes luma blocks Y included in the imageinput through the input terminal IN4 according to a predeterminedencoding mode of each of the luma blocks Y. The input terminal IN4 isidentical to the input terminal IN2 illustrated in FIG. 2.

According to an embodiment of the present invention, the second encodingunit 514 encodes chroma blocks Cb or Cr included in the image inputthrough the input terminal IN4 according to a majority of encoding modesamong the predetermined encoding modes of the luma blocks Y. The imagemay have one of the 4:2:0 format, the 4:2:2 format, and the 4:4:4format.

According to another embodiment of the present invention, the secondencoding unit 514 encodes the chroma blocks Cb or Cr included in theimage input through the input terminal IN4 according to a predeterminedencoding mode of each of the chroma blocks Cb or Cr. The image may haveone of the 4:2:0 format, the 4:2:2 format, and the 4:4:4 format.

The encoding mode used to encode the chroma blocks Cb or Cr included inthe image may be already determined before the image is input to themotion estimating unit 212 or the motion compensating unit 216.

According to another embodiment of the present invention, the secondencoding unit 514 encodes the chroma block Cb or Cr included in theimage input through the input terminal IN4 according to an encoding modeof a luma block having the same phase as that of the chroma block Cb orCr. The image may have one of the 4:2:2 format and the 4:4:4 format.

In the above embodiments of the present invention, the encoding modeused to encode each of the luma blocks Y included in the image may bealready determined when the image is input through the input terminalIN4. Similarly, in the second embodiment of the present invention, theencoding mode used to encode each of the luma blocks, each of the bluechroma blocks Cb, and each of the red chroma blocks Cr included in theimage may be already determined when the image is input through theinput terminal IN4. The image and mode information are input into theinput terminal IN4. The mode information indicates the encoding mode (ora decoding mode). The encoding mode (or the decoding mode) can be aninter mode or an intra mode.

A motion information generating unit (not shown) may be included in theimage encoding apparatus of an embodiment of the present invention andmay generate motion information. The motion information generating unitmay generate motion information on some of the luma blocks encoded bythe first encoding unit 512. Likewise, the motion information generatingunit may generate motion information on some of the chroma blocksencoded by the second encoding unit 514.

The motion information includes the mode information and a coded blockpattern (CBP). If the mode information indicates the inter mode, themotion information also includes information on a motion vector.

The CBP indicates whether the results of the quantization include avalue other than 0. The image encoding apparatus of an embodiment of thepresent invention can include a CBP generating unit (not shown). Everytime a block is completely quantized by the quantizing unit 220, the CBPgenerating unit (not shown) checks whether a result of the quantizationincludes a value other than 0, if the result of the quantizationincludes a value other than 0, generates 1 as the CBP of the block, and,if the result of the quantization does not include a value other than 0,generates 0 as the CBP of the block.

The motion information generating unit (not shown) generates the motioninformation including the mode information input through the inputterminal IN4 and the CBP generated by the CBP generating unit.

The third encoding unit 516 encodes the motion information generated bythe motion information generating unit.

The bitstream generating unit 518 is realized by the entropy encodingunit 230.

The bitstream generating unit 518 generates a bitstream by combining theresults of the encoding performed by the first encoding unit 512, theresults of the encoding performed by the second encoding unit 514, andthe results of the encoding performed by the third encoding unit 516 andoutputs the bitstream through an output terminal OUT5. The outputterminal OUT5 is identical to the output terminal OUT2 illustrated inFIG. 2.

FIGS. 6 through 8 are diagrams for explaining motion information (MI).Referring to FIGS. 6 through 8, the MI can be included in each block orin some of the blocks.

Referring to FIG. 6A, the macroblock of the 4:2:0 format imageillustrated in FIG. 4A includes first through sixth blocks 612, 614,616, 618, 620, and 630.

Referring to FIG. 6B, MI on the macroblock illustrated in FIG. 6A isexpressed as bitstream 640. MI(t) (t denotes positive numbers between 1and 6, 1≦t≦6) indicates MI on a u^(th) block generated by the motioninformation generating unit.

Referring to FIG. 7A, the macroblock of the 4:2:2 format imageillustrated in FIG. 4B includes first through eighth blocks 712, 714,716, 718, 720, 722, 724, and 726.

Referring to FIG. 7B, MI on the macroblock illustrated in FIG. 7A isexpressed as bitstream 730. MI(u) (u denotes positive numbers between 1and 8, 1≦u≦8) indicates MI on a u^(th) block generated by the motioninformation generating unit.

Referring to FIG. 8A, the macroblock of the 4:4:4 format imageillustrated in FIG. 4C includes first through twelfth blocks 812, 814,816, 818, 820, 822, 824, 826, 828, 830, 832, and 834.

Referring to FIG. 8B, MI on the macroblock illustrated in FIG. 8A isexpressed as bitstream 730. MI(v) (v denotes positive numbers between 1and 12, 1≦v≦12) indicates MI on a v^(th) block generated by the motioninformation generating unit.

FIG. 9 is a block diagram of an image decoding apparatus according to anembodiment of the present invention. Referring to FIG. 9, the imagedecoding apparatus comprises a third decoding unit 910, a first decodingunit 920, and a second decoding unit 930.

The third decoding unit 910 extracts motion information from thebitstream input through the input terminal IN5, and decodes theextracted motion information. The input terminal IN5 is identical to theinput terminal IN3 illustrated in FIG. 3.

The first decoding unit 920 and the second decoding unit 930 arerealized by using the decoding unit 120 comprising the entropy decodingunit 312, the zero decoding unit 314, the inverse rearranging unit 316,the dequantizing unit 318, the inverse spatial converting unit 320, themotion estimating unit 322, and the reference image storing unit 324.

The first decoding unit 920 indicates the decoding unit 120 that decodesluma blocks Y. Likewise, the second decoding unit 930 indicates thedecoding unit 120 that decodes chroma blocks Cb or Cr.

The first decoding unit 920 decodes the luma blocks Y according to apredetermined decoding mode of each of the luma blocks Y. In detail, thepredetermined decoding mode is already represented in the bitstreaminput through the input terminal IN5.

Therefore, the first decoding unit 920 checks whether MI decoded by thethird decoding unit 910 includes MI on a luma block that is to bedecoded.

If it is determined that the MI decoded by the third decoding unit 910does not include MI on the luma block that is to be decoded, the firstdecoding unit 920 decodes the luma block that is to be decoded accordingto a constant decoding mode. The constant decoding mode can be an intermode or an intra mode.

To the contrary, if it is determined that the MI decoded by the thirddecoding unit 910 includes MI on the luma block that is to be decoded,the first decoding unit 920 analyzes whether mode information includedin the decoded MI indicates the inter mode or the intra mode as thedecoding mode. In this regard, the first decoding unit 920 decodes theluma block that is to be decoded according to the analyzed decodingmode.

According to an embodiment of the present invention, the second decodingunit 930 decodes the chroma blocks Cb or Cr included in an imageaccording to a majority of decoding modes among the predetermineddecoding modes of the luma blocks Y. The image may have one of the 4:2:0format, the 4:2:2 format, and the 4:4:4 format.

According to another embodiment of the present invention, the seconddecoding unit 930 decodes the chroma blocks Cb or Cr included in theimage according to a predetermined decoding mode of each of the chromablocks Cb or Cr. The image may have one of the 4:2:0 format, the 4:2:2format, and the 4:4:4 format.

In detail, the predetermined decoding mode is already represented in thebitstream input through the input terminal IN5.

Therefore, the second decoding unit 930 checks whether the MI decoded bythe third decoding unit 910 includes MI on a chroma block that is to bedecoded.

If it is determined that the MI decoded by the third decoding unit 910does not include MI on the chroma block that is to be decoded, thesecond decoding unit 930 decodes the chroma block that is to be decodedaccording to a constant decoding mode. The constant decoding mode can bethe inter mode or the intra mode.

To the contrary, if it is determined that the MI decoded by the thirddecoding unit 910 includes MI on the chroma block that is to be decoded,the second decoding unit 930 analyzes whether the mode informationincluded in the decoded MI indicates the inter mode or the intra mode asthe decoding mode. In this regard, the second decoding unit 930 decodesthe chroma block to be decoded according to the analyzed decoding mode.

According to another embodiment of the present invention, the seconddecoding unit 930 decodes the chroma blocks Cb or Cr included in theimage according to a decoding mode of a luma block having the same phaseas that of the chroma block Cb or Cr. The image may have one of the4:2:2 format and the 4:4:4 format.

The luma blocks decoded by the first decoding unit 920 and the chromablocks decoded by the second decoding unit 930 are output through anoutput terminal OUT6. The output terminal 6 is identical to the outputterminal OUT3 or OUT4 illustrated in FIG. 3.

FIGS. 10A and 10B are diagrams for explaining the principle ofencoding/decoding an image using a 1 motion vector (MV). The 1 MVindicates an encoding/decoding method used when a macroblock needs 1 MVat the most. For convenience of explanation, referring to FIGS. 10A and10B, the blocks have a 4:2:0 image format.

If the blocks are encoded/decoded using the 1 MV, luma blocks 1012,1014, 1016, 1018, 1032, 1034, 1036, and 1038, blue chroma blocks 1020and 1040, and red chroma blocks 1022 and 1042 have the same encodingmode (or the same decoding mode).

FIG. 11 is a flowchart illustrating an image encoding method accordingto an embodiment of the present invention. Referring to FIG. 11, theimage encoding method comprises operations 1110 through 1140 of encodingluma blocks and then encoding chroma blocks according to encoding modesdetermined based on encoding modes of the luma blocks.

The first encoding unit 512 encodes the luma blocks according topredetermined encoding modes (Operation 1110).

The second encoding unit 514 encodes the chroma blocks according to amajority of encoding modes among the predetermined decoding modes of theluma blocks (Operations 1120 through 1140).

In detail, the second encoding unit 514 determines whether more thanhalf of the predetermined encoding modes of the luma blocks are intermodes (Operation 1120). In Operation 1120, the second encoding unit 514can determine whether more than half of the predetermined encoding modesof the luma blocks are inter modes. Or in Operation 1120, unlike FIG.11, the second encoding unit 514 can determine whether more than half ofthe predetermined encoding modes of the luma blocks are intra modes.

If the second encoding unit 514 determines that more than half of thepredetermined encoding modes of the luma blocks are inter modes inOperation 1120, the second encoding unit 514 encodes the chroma blocksaccording to an inter mode (Operation 1130). If the second encoding unit514 determines that more than half of the predetermined encoding modesof the luma blocks are not inter modes in Operation 1120, the secondencoding unit 514 encodes the chroma blocks according to an intra mode(Operation 1140).

FIG. 12 is a flowchart illustrating an image decoding method accordingto an embodiment of the present invention. Referring to FIG. 12, theimage decoding method comprises operations 1210 through 1232 of decodingluma blocks and then decoding chroma blocks according to decoding modesdetermined based on decoding modes of the luma blocks.

The third decoding unit 910 decodes MI (Operation 1210). The firstdecoding unit 920 determines whether a block that is to be decoded is aluma block (Operation 1212).

N denotes a decoding priority and can be t, u, or v as described above.

If the first decoding unit 920 determines in Operation 1212 that theblock that is to be decoded is the luma block, the first decoding unit920 determines whether MI on the block that is to be decoded is includedin the MI decoded in Operation 1210 (Operation 1214).

If the first decoding unit 920 determines that the MI on the block thatis to be decoded is not included in the decoded MI, the first decodingunit 920 decodes the blocks that are to be decoded according to an intermode (Operation 1216). Unlike Operation 1216, the first decoding unit920 can decode the block that is to be decoded according to an intramode.

If the first decoding unit 920 determines that the MI on the block thatis to be decoded is included in the decoded MI, the first decoding unit920 analyzes the MI on the block that is to be decoded (Operation 1218).

The first decoding unit determines whether the MI analyzed in Operation1218 is the intra mode (Operation 1220).

If the first decoding unit 920 determines in Operation 1220 that the MIis the intra mode, the first decoding unit 920 decodes the block that isto be decoded according to the intra mode (Operation 1222). To thecontrary, if the first decoding unit 920 determines in Operation 1220that the MI is the inter mode, the first decoding unit 920 performsOperation 1216.

If the first decoding unit 920 determines in Operation 1212 that theblock that is to be decoded is a chroma block, the second decoding unit930 determines whether more than half of the decoding modes of all lumablocks included in the same macroblock as the block that is to bedecoded are inter modes (Operation 1224).

Unlike FIG. 12, the second decoding unit 930 can determine whether morethan half of the decoding modes of all luma blocks included in the samemacroblock as the block that is to be decoded are intra modes inOperation 1224.

If the second decoding unit 930 determines in Operation 1224 that morethan half of the decoding modes of all luma blocks included in the samemacroblock as the block that is to be decoded are not inter modes, thesecond decoding unit 930 decodes the block to be decoded according tothe intra mode (Operation 1226).

If the second decoding unit 930 determines in Operation 1224 that morethan half of the decoding modes of all luma blocks included in the samemacroblock as the block that is to be decoded are inter modes, thesecond decoding unit 930 decodes the block to be decoded according tothe inter mode (Operation 1228).

It is checked whether all the blocks of the macroblock are decoded(Operation 1230). If it is determined that the macroblock has undecodedblocks, Operations 1232 and 1212 are performed.

FIGS. 13 through 15 are diagrams for explaining the principle ofencoding/decoding an image using a 4 MV according to an embodiment ofthe present invention. The 4 MV indicates an encoding/decoding methodwhen a macroblock needs 4 MVs at the most. Referring to FIGS. 13A and13B, the macroblocks have a 4:2:0 image format.

Referring to FIG. 13A, luma blocks 1312, 1314, 1316, and 1318 areencoded/decoded according to an intra mode, an inter mode, an intermode, and an inter mode, respectively. A majority of encoding modes (ordecoding modes) among encoding modes (or decoding modes) of the lumablocks 1312, 1314, 1316, and 1318 are inter modes. Therefore, a bluechroma block 1320 is encoded/decoded according to the inter mode.Likewise, a red chroma block 1330 is encoded/decoded according to theinter mode.

Similarly, referring to FIG. 13B, luma blocks 1342, 1344, 1346, and 1348are encoded/decoded according to an intra mode, an intra mode, an intramode, and an inter mode, respectively. A majority of encoding modes (ordecoding modes) among encoding modes (or decoding modes) of the lumablocks 1342, 1344, 1346, and 1348 are intra modes. Therefore, a bluechroma block 1350 is encoded/decoded according to the intra mode.Likewise, a red chroma block 1360 is encoded/decoded according to theintra mode.

Referring to FIGS. 14A and 14B, the macroblocks have a 4:2:2 imageformat. Referring to FIG. 14A, luma blocks 1412, 1414, 1416, and 1418are encoded/decoded according to an intra mode, an inter mode, an intermode, and an inter mode, respectively. A majority of encoding modes (ordecoding modes) among encoding modes (or decoding modes) of the lumablocks 1412, 1414, 1416, and 1418 are inter modes. Therefore, bluechroma blocks 1422 and 1424 is encoded/decoded according to the intermode. Likewise, red chroma blocks 1432 and 1434 are encoded/decodedaccording to the inter mode.

Similarly, referring to FIG. 14B, luma blocks 1442, 1444, 1446, and 1448are encoded/decoded according to an intra mode, an intra mode, an intramode, and an inter mode, respectively. A majority of encoding modes (ordecoding modes) among encoding modes (or decoding modes) of the lumablocks 1442, 1444, 1446, and 1448 are intra modes. Therefore, bluechroma blocks 1452 and 1454 are encoded/decoded according to the intramode. Likewise, red chroma blocks 1462 and 1464 are encoded/decodedaccording to the intra mode.

Referring to FIGS. 15A and 15B, the macroblocks have a 4:4:4 imageformat. Referring to FIG. 15A, luma blocks 1512, 1514, 1516, and 1518are encoded/decoded according to an intra mode, an inter mode, an intermode, and an inter mode, respectively. A majority of encoding modes (ordecoding modes) among encoding modes (or decoding modes) of the lumablocks 1512, 1514, 1516, and 1518 are inter modes. Therefore, bluechroma blocks 1522, 1524, 1526, and 1528 are encoded/decoded accordingto the inter mode. Likewise, red chroma blocks 1432, 1534, 1536, and1538 are encoded/decoded according to the inter mode.

Similarly, referring to FIG. 15B, luma blocks 1542, 1544, 1546, and 1548are encoded/decoded according to an intra mode, an intra mode, an intramode, and an inter mode, respectively. A majority of encoding modes (ordecoding modes) among encoding modes (or decoding modes) of the lumablocks 1542, 1544, 1546, and 1548 are intra modes. Therefore, bluechroma blocks 1552, 1554, 1556, and 1558 are encoded/decoded accordingto the intra mode. Likewise, red chroma blocks 1562, 1564, 1566, and1568 are encoded/decoded according to the intra mode.

FIG. 16 is a flowchart illustrating an image encoding method accordingto another embodiment of the present invention. Referring to FIG. 16,the first encoding unit 512 encodes luma blocks according to apredetermined encoding mode of each luma block (Operation 1610). Thesecond encoding unit 514 encodes chroma blocks according to apredetermined encoding mode of each chroma block (Operation 1620).

Operation 1620 can be performed after Operation 1610 has been performed,before Operation 1610 has been performed, or simultaneously whileOperation 1610 is being performed.

FIG. 17 is a flowchart illustrating an image decoding method accordingto another embodiment of the present invention. Referring to FIG. 17,the image decoding method comprises operations 1710 through 1724 ofdecoding luma blocks according to a predetermined decoding mode of eachluma block and decoding chroma blocks according to a predetermineddecoding mode of each chroma block.

The third decoding unit 910 decodes MI (Operation 1710).

The first decoding unit 920 or the second decoding unit 930 determineswhether MI on block that is to be decoded is included in the MI decodedin Operation 1710 (Operation 1712).

If the first decoding unit 920 or the second decoding unit 930determines that the MI on the block that is to be decoded is included inthe decoded MI, the first decoding unit 920 or the second decoding unit930 analyzes the MI on the block that is to be decoded (Operation 1714).

The first decoding unit 920 or the second decoding unit 930 determineswhether the MI analyzed in Operation 1714 is an intra mode (Operation1716).

If the first decoding unit 920 or the second decoding unit 930determines in Operation 1716 that the MI is the intra mode, the firstdecoding unit 920 or the second decoding unit 930 decodes the block thatis to be decoded according to the intra mode (Operation 1718). To thecontrary, if the first decoding unit 920 or the second decoding unit 930determines in Operation 1716 that the MI is not an intra mode, the firstdecoding unit 920 or the second decoding unit 930 decodes the block thatis to be decoded according to the inter mode (Operation 1720).

If the first decoding unit 920 or the second decoding unit 930determines that the MI on block that is to be decoded is not included inthe MI decoded in Operation 1710, the first decoding unit 920 or thesecond decoding unit 930 can perform Operation 1720 or decode the blockthat is to be decoded according to the intra mode.

FIGS. 18A, 18B, and 18C are diagrams for explaining the principle ofencoding/decoding an image using a 4 MV according to another embodimentof the present invention.

Referring to FIG. 18A, a macroblock has a 4:2:0 image format. Lumablocks 1812, 1814, 1816, and 1818 are encoded/decoded according to anintra mode, an inter mode, an inter mode, and an inter mode,respectively. A blue chroma block 1820 is encoded/decoded according tothe inter mode. A red chroma block 1830 is encoded/decoded according tothe inter mode. Therefore, the encoding modes (or the decoding modes) ofthe luma blocks 1812, 1814, 1816, and 1818, the blue chroma block 1820,and the red chroma block 1830 cannot be related to each other.

Referring to FIG. 18B, a macroblock has a 4:2:2 image format. Lumablocks 1842, 1844, 1846, and 1848 are encoded/decoded according to anintra mode, an intra mode, an intra mode, and an inter mode,respectively. Blue chroma blocks 1852 and 1854 is encoded/decodedaccording to the inter mode and the intra mode, respectively. Red chromablocks 1862 and 1864 are encoded/decoded according to the intra mode andthe inter mode, respectively. Therefore, the encoding modes (or thedecoding modes) of the luma blocks 1842, 1844, 1846, and 1848, the bluechroma blocks 1852 and 1854, and the red chroma blocks 1862 and 1864cannot be related to each other.

Referring to FIG. 18C, a macroblock has a 4:4:4 image format. Lumablocks 1872, 1874, 1876, and 1878 are encoded/decoded according to anintra mode, an intra mode, an intra mode, and an inter mode,respectively. Blue chroma blocks 1882, 1884, 1886, and 1888 areencoded/decoded according to the inter mode, the intra mode, the intramode, and the inter mode, respectively. Red chroma blocks 1892, 1894,1896, and 1898 are encoded/decoded according to the inter mode.Therefore, the encoding modes (or the decoding modes) of the luma blocks1842, 1844, 1846, and 1848, the blue chroma blocks 1852 and 1854, andthe red chroma blocks 1862 and 1864 cannot be related to each other.

FIG. 19 is a flowchart illustrating an image encoding method accordingto another embodiment of the present invention. Referring to FIG. 19,the image encoding method comprises Operations 1910 through 1920 ofencoding luma blocks and then encoding chroma blocks according toencoding modes determined based on encoding modes of the luma blocks.

The first encoding unit 512 encodes each luma block according to apredetermined encoding mode (Operation 1910).

The second encoding unit 514 encodes each chroma block according to theencoding mode of each luma block having the same phase as each chromablock (Operations 1920).

FIG. 20 is a flowchart illustrating an image decoding method accordingto another embodiment of the present invention. Referring to FIG. 20,the image decoding method comprises Operations 2010 through 2032 ofdecoding luma blocks and then decoding chroma blocks according todecoding modes determined based on decoding modes of the luma blocks.

The third decoding unit 910 decodes MI (Operation 2010). The firstdecoding unit 920 determines whether block to be decoded is a luma block(Operation 2012).

N denotes a decoding priority and can be t, u, or v as described above.

If the first decoding unit 920 determines in Operation 2012 that theblock to be decoded is the luma block, the first decoding unit 920determines whether MI on the block that is to be decoded is included inthe MI decoded in Operation 2010 (Operation 2014).

If the first decoding unit 920 determines in Operation 2014 that the MIon the blocks that are to be decoded is included in the decoded MI, thefirst decoding unit 920 analyzes the MI on the blocks that are to bedecoded (Operation 2016).

The first decoding unit 920 determines whether the MI analyzed inOperation 2016 is an intra mode (Operation 2018).

If the first decoding unit 920 determines in Operation 2018 that the MIis the intra mode, the first decoding unit 920 decodes the block that isto be decoded according to the intra mode (Operation 2020). To thecontrary, if the first decoding unit 920 determines in Operation 2018that the MI is not an intra mode, the first decoding unit 920 decodesthe block that is to be decoded according to the inter mode (Operation2022).

If the first decoding unit 920 determines in Operation 2014 that the MIon the block to be decoded is not included in the decoded MI, the firstdecoding unit 920 performs Operation 2022 or can decode the block thatis to be decoded according to the inter mode, although this case is notshown.

If the first decoding unit 920 determines in Operation 2012 that theblock to be decoded are a chroma block, the second decoding unit 930determines whether the decoding mode of the luma blocks having the samephase as the block that is to be decoded is the inter mode or intra mode(Operation 2024).

If the second decoding unit 930 determines in Operation 2024 that thedecoding mode of the luma blocks having the same phase as the block thatis to be decoded is the inter mode, the second decoding unit 930 decodesthe block that is to be decoded according to the inter mode (Operation2026). To the contrary, if the second decoding unit 930 determines inOperation 2024 that the decoding mode of the luma blocks having the samephase as the block that is to be decoded is the intra mode, the seconddecoding unit 930 decodes the block to be decoded according to the intramode (Operation 2028).

After Operations 2020, 2022, 2026 or 2028 are performed, it isdetermined whether all the blocks of the macroblock are decoded(Operation 2030). If it is determined in Operation 2030 that themacroblock has undecoded blocks, a next block that is to be next-decodedin Operations 2032 and 2012.

FIGS. 21A and 22B are diagrams for explaining the principle ofencoding/decoding an image using a 4 MV according to another embodimentof the present invention.

Referring to FIG. 21A, a macroblock has a 4:2:2 image format. A phase ofone of luma blocks 2112, 2114, 2116, and 2118 indicates a position ofone of the luma blocks 2112, 2114, 2116, and 2118 in the luma blocks2112, 2114, 2116, and 2118. A phase of one of blue chroma blocks 2122and 2124 indicates a position of one of the blue chroma blocks 2122 and2124 in blue chroma blocks 2122, 2124, 2132, and 2134. A phase of one ofred chroma blocks 2132 and 2134 indicates a position of one of the redchroma blocks 2132 and 2134 in the red chroma blocks 2122, 2124, 2132,and 2134.

The luma blocks 2112, 2114, 2116, and 2118 are encoded/decoded accordingto an intra mode, an intra mode, an intra mode, and an inter mode,respectively.

Therefore, the blue chroma block 2122 is encoded/decoded according tothe encoding mode (or the decoding mode) of the luma block 2112, theblue chroma block 2124 is encoded/decoded according to the encoding mode(or the decoding mode) of the luma block 2116, the red chroma block 2132is encoded/decoded according to the encoding mode (or the decoding mode)of the luma block 2114, and the red chroma block 2134 is encoded/decodedaccording to the encoding mode (or the decoding mode) of the luma block2118.

Referring to FIG. 21B, a macroblock has a 4:4:4 image format. A phase ofone of luma blocks 2142, 2144, 2146, and 2148 indicates a position ofone of the luma blocks 2142, 2144, 2146, and 2148 in the luma blocks2142, 2144, 2146, and 2148. A phase of one of blue chroma blocks 2152,2154, 2156, and 2158 indicates a position of one of the blue chromablocks 2152, 2154, 2156, and 2158 in the blue chroma blocks 2152, 2154,2156, and 2158. A phase of one of red chroma blocks 2162, 2164, 2166,and 2168 indicates a position of one of the red chroma blocks 2162,2164, 2166, and 2168 in the red chroma blocks 2162, 2164, 2166, and2168.

The luma blocks 2142, 2144, 2146, and 2148 are encoded/decoded accordingto an intra mode, an intra mode, an intra mode, and an inter mode,respectively.

Therefore, the blue chroma block 2152 is encoded/decoded according tothe encoding mode (or the decoding mode) of the luma block 2142, theblue chroma block 2154 is encoded/decoded according to the encoding mode(or the decoding mode) of the luma block 2144, the blue chroma block2156 is encoded/decoded according to the encoding mode (or the decodingmode) of the luma block 2146, and the blue chroma block 2158 isencoded/decoded according to the encoding mode (or the decoding mode) ofthe luma block 2148.

Similarly, the red chroma block 2162 is encoded/decoded according to theencoding mode (or the decoding mode) of the luma block 2142, and the redchroma block 2164 is encoded/decoded according to the encoding mode (orthe decoding mode) of the luma block 2144, the red chroma block 2166 isencoded/decoded according to the encoding mode (or the decoding mode) ofthe luma block 2146, and the red chroma block 2168 is encoded/decodedaccording to the encoding mode (or the decoding mode) of the luma block2148.

The present invention can also be embodied as computer readable code ona computer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, and carrier waves. The computer readable recording medium canalso be distributed network coupled computer systems so that thecomputer readable code is stored and executed in a distributed fashion.

According to the image encoding method and apparatus of the presentinvention, an encoding unit that encodes an image using a 4 MV encodeschroma blocks according to encoding modes determined based on apredetermined encoding mode of each luma block. Similarly, according tothe image decoding method and apparatus of the present invention, adecoding unit that decodes an image using a 4 MV decodes chroma blocksaccording to decoding modes determined based on a predetermined decodingmode of each luma block.

According to the method and apparatus for encoding an image of thepresent invention, an encoding unit that encodes an image using a 4 MVencodes luma blocks according to encoding modes determined based on apredetermined encoding mode of each luma block, and encodes chromablocks according to encoding modes determined based on a predeterminedencoding mode of each chroma block. Similarly, according to the methodand apparatus for decoding an image of the present invention, a decodingunit that decodes an image using a 4MV decodes luma blocks according todecoding modes determined based on a predetermined decoding mode of eachluma block, and decodes chroma blocks according to decoding modesdetermined based on a predetermined decoding mode of each chroma block.

The method and apparatus for encoding and decoding an image of thepresent invention provides a variety of methods of determining encodingmodes (or decoding modes) when an image that is to be compressed (orthat is to be restored) is expressed as a luma component and a chromacomponent.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. An image decoding method comprising: (a) decoding luma blocksaccording to a predetermined decoding mode of each luma block; and (b)decoding chroma blocks according to the predetermined decoding mode ofeach luma blocks.
 2. The image decoding method of claim 1, wherein, inoperation (b), the chroma blocks are decoded according to a majority ofdecoding modes among the predetermined decoding modes of the lumablocks.
 3. The image decoding method of claim 2, wherein the luma blocksand the chroma blocks have one of a 4:2:0 image format, a 4:2:2 imageformat, and a 4:4:4 image format.
 4. The image decoding method of claim1, wherein, in operation (b), the chroma block is decoded according tothe decoding mode of the luma block having the same phase as the chromablock.
 5. The image decoding method of claim 4, wherein the luma blocksand the chroma blocks have one of the 4:2:2 image format and the 4:4:4image format.
 6. An image decoding method comprising: (a) decoding lumablocks according to a predetermined decoding mode of each luma block;and (b) decoding chroma blocks according to a predetermined decodingmode of each chroma block.
 7. The image decoding method of claim 6,wherein the luma blocks and the chroma blocks have one of a 4:2:0 imageformat, a 4:2:2 image format, and a 4:4:4 image format.
 8. The imagedecoding method of claim 1 or 6, wherein operation (a) comprises: (a1)determining whether given motion information (MI) indicates a decodingmode of the luma block to be decoded; and (a2) if it is determined thatthe MI indicates the decoding mode of the luma block to be decoded,decoding the luma block to be decoded according to the decoding moderepresented in the MI.
 9. The image decoding method of claim 8, whereinif it is determined in operation (a1) that the MI does not indicate thedecoding mode of the luma block to be decoded, operation (a) furthercomprises: decoding the luma block to be decoded according to constantdecoding mode.
 10. The image decoding method of claim 6, whereinoperation (b) comprises: (b1) determining whether given MI indicates adecoding mode of the chroma block to be decoded; and (a2) if it isdetermined that the MI indicates the decoding mode of the chroma blockto be decoded, decoding the chroma block to be decoded according to thedecoding mode represented in the MI.
 11. The image decoding method ofclaim 10, wherein if it is determined in operation (b1) that the MI doesnot indicate the decoding mode of the chroma block to be decoded,operation (b) further comprises: decoding the chroma block to be decodedaccording to constant decoding mode.
 12. An image encoding methodcomprising: (a) encoding luma blocks according to a predeterminedencoding mode of each luma block; and (b) encoding chroma blocksaccording to the predetermined encoding mode of each luma block.
 13. Theimage encoding method of claim 12, wherein, in operation (b), the chromablocks are encoded according to a majority of encoding modes among thepredetermined encoding modes of the luma blocks.
 14. The image encodingmethod of claim 12, wherein, in operation (b), the chroma block isencoded according to the encoding mode of the luma block having the samephase as the chroma block.
 15. An image encoding method comprising: (a)encoding luma blocks according to a predetermined encoding mode of eachluma block; and (b) encoding chroma blocks according to a predeterminedencoding mode of each chroma block.
 16. An image decoding apparatuscomprising: a first decoding unit decoding luma blocks according to apredetermined decoding mode of each luma block; and a second decodingunit decoding chroma blocks according to the predetermined decoding modeof each luma block.
 17. The image decoding apparatus of claim 16,wherein the second decoding unit decodes the chroma blocks according toa majority of decoding modes among the predetermined decoding modes ofthe luma blocks.
 18. The image decoding apparatus of claim 17, whereinthe luma blocks and the chroma blocks have one of a 4:2:0 image format,a 4:2:2 image format, and a 4:4:4 image format.
 19. The image decodingapparatus of claim 16, wherein the second decoding unit decodes thechroma block according to the decoding mode of the luma block having thesame phase as the chroma block.
 20. The image decoding apparatus ofclaim 19, wherein the luma blocks and the chroma blocks have one of the4:2:2 image format and the 4:4:4 image format.
 21. An image decodingapparatus comprising: a first decoding unit decoding luma blocksaccording to a predetermined decoding mode of each luma block; and asecond decoding unit decoding chroma blocks according to a predetermineddecoding mode of each chroma block.
 22. The image decoding apparatus ofclaim 21, wherein the luma blocks and the chroma blocks have one of a4:2:0 image format, a 4:2:2 image format, and a 4:4:4 image format. 23.An image encoding apparatus comprising: a first encoding unit encodingluma blocks according to a predetermined encoding mode of each lumablock; and a second encoding unit encoding chroma blocks according tothe predetermined encoding mode of each luma block.
 24. The imageencoding apparatus of claim 23, wherein the second encoding unit encodesthe chroma blocks according to a majority of encoding modes among thepredetermined encoding modes of the luma blocks.
 25. The image encodingapparatus of claim 23, wherein the second encoding unit encodes thechroma block according to the encoding mode of the luma block having thesame phase as the chroma block.
 26. An image encoding apparatuscomprising: a first encoding unit encoding luma blocks according to apredetermined encoding mode of each luma block; and a second encodingunit encoding chroma blocks according to a predetermined encoding modeof each chroma block.